EP 0 419 455 B1 discloses a control system for triggering a restraining means in a motor vehicle in which a sensor device supplies a longitudinal acceleration signal and a transverse acceleration signal. A triggering signal for the restraining means for protection against head-on impacts is generated as a function of the longitudinal acceleration signal and the transverse acceleration signal by a downstream evaluation device of the control system.
A control system for triggering a restraining means in a motor vehicle is disclosed in U.S. Pat. No. 4,933,570. A triggering signal for the restraining means is generated as a function of a signal supplied by an acceleration sensor and a switching signal of a mechanical acceleration switch. Such sensors, which are embodied as acceleration switches and referred to as safing sensors, ensure that the triggering of the restraining means is prevented if the acceleration sensor or the evaluation device operates incorrectly and consequently supplies a faulty triggering signal. Such an acceleration switch in the firing circuit usually has a low response threshold and as a result supplies a time window within which triggering can take place on the basis of an evaluation of the signals supplied by the acceleration sensor.
Multi-channel control systems for vehicle occupant protection, i.e. in control systems having a plurality of differently oriented acceleration sensors, each individual sensor can be assigned a redundant sensor with the properties of a safing sensorxe2x80x94for example a mechanical acceleration switch. In a control system with two channels, four acceleration sensors/switches would consequently be necessary in order to be able to detect the failure of a channel. Such a control system with four acceleration sensors is costly in terms of components and requires a large installation space owing to the safing sensors which continue to have relatively large dimensions.
DE 196 45 952 A1 discloses a control system for triggering a restraining means in a motor vehicle which has a sensor device with three longitudinal acceleration sensors. The acceleration sensors are arranged in a star shape such that they each have differently oriented sensitivity axes. In a downstream evaluation device it is possible to determine the direction and the strength of an acceleration acting on the vehicle from the signals of only two of the three acceleration sensors. The signal of the third acceleration sensor is used here to check one of the two calculated variables, the direction or the strength of the acceleration acting on the vehicle.. The third sensor assumes the function of a safing sensor, and can prevent the triggering of the restraining means if the value made available by it deviates significantly from a value calculated beforehand from the signals of the two other sensors.
In one embodiment of the invention, there is a control system for a vehicle occupant protection device in a motor vehicle, a sensor device having at least one acceleration sensor with two sensitivity axes which are perpendicular to one another and which lie in a plane parallel to a plane defined approximately by a vehicle longitudinal axis and a vehicle transverse axis; and an additional acceleration sensor with a sensitivity axis which lies parallel to the plane which is parallel to the plane defined by the vehicle longitudinal axis and the vehicle transverse axis; the sensitivity axis of said acceleration sensor enclosing with one of the sensitivity axes of the acceleration sensor an angle which can have a value between 15xc2x0 and 75xc2x0; an evaluation device to evaluate acceleration signals which are supplied by the acceleration sensor, and to generate a triggering signal to trigger the vehicle occupant protection device; and a switching unit which is connected to the evaluation device and outputs a firing signal as a function of the triggering signal and another signal, wherein a reference value is formed from the acceleration signals of the acceleration sensor in a safing evaluation unit, and wherein the acceleration sensor is an X-Y acceleration sensor, in the case of a significant deviation of an acceleration signal supplied by the additional acceleration sensor from the reference value, a disable signal is generated and supplied to the switching unit which prevents the firing signal for triggering the vehicle occupant protection device from being output even if a triggering signal is generated by the evaluation device, and a threshold value is formed in the safing evaluation unit from at least one of the received acceleration signals, and in that the:disable signal is prevented from being output to the switching unit only if the threshold value is exceeded by at least one of the acceleration signals.
In one aspect of the invention, a direction and a strength of an acceleration acting on the motor vehicle are determined in the evaluation device from the acceleration signals supplied by the X-Y acceleration sensor, and an acceleration signal which is supplied by the acceleration sensor and generates a fault situation signal is used if a significant difference is detected with respect to the direction and the strength from the acceleration signals.
In another aspect of the invention, the acceleration signal which is generated by the acceleration sensor is compared with the acceleration signals in a safing evaluation unit.
In still another aspect of the invention, the reference value is formed in the safing evaluation unit from the acceleration signals of the X-Y acceleration sensor, and a fault situation signal which is generated when there is a significant deviation of the acceleration signal from the reference value preventings the triggering of the vehicle occupant protection device.
In yet another aspect of the invention, the fault situation signal is a disable signal which is supplied to the switching unit and prevents a firing signal for the vehicle occupant protection device from being output even if a triggering signal is generated by the evaluation device.
In another aspect of the invention, the disable signal simultaneously triggers a warning device of the vehicle occupant protection device.